1. Field of the Invention
The invention relates to computer busing techniques, and more specifically to implementation on a host bus of devices intended for a standard peripheral bus.
2. Description of the Related Art
With the surge in development of network based microcomputer systems, network servers have been called upon to process and transfer ever greater amounts of data. This data movement has historically relied upon SCSI controllers accessing disk arrays, as well as network interface controllers for accessing networks.
These controllers have typically been placed on an EISA bus accessed by the microprocessor through an EISA bus controller. As speeds have increased, however, and as greater demands have been placed on the data throughput of these servers, it has become more and more desirable to move these SCSI controllers and network interface controllers directly to the host bus of a microcomputer system. A host bus typically has more bandwidth and allows for more direct data transfers between a microprocessor and these communications devices, as well as permitting direct data transfer between local memory and these devices.
But a great deal of system software has been written to access SCSI and network interface controllers as being present on an EISA bus. This system software relies on these devices being logically present on the EISA bus, with memory mapped and input/output (I/O) registers appearing in the EISA address space and being accessed using commands directed to that address space. Further, many of the host bus devices, such as memory controllers and EISA bus controllers, assume that either the memory controller or the EISA bus controller will execute the cycle provided by the processor. No provisions are made for local devices. It would therefore be greatly desirable to allow implementation of various EISA devices on a host bus without necessitating changes to system software to access those devices or major modification to existing memory or EISA bus controllers.